The Gunners broke their transfer record to bring in a France international over the summer, before their London rivals at Stamford Bridge did likewise when luring a Spanish frontman away from Real Madrid.
Both have hit the ground running to offer an immediate return on the sizeable investment made in their talent.
Morata slightly edges things at present, with three goals in five appearances compared to Lacazette’s return of two, and Merson believes the 24-year-old will prove to be a shrewd addition for the Blues and the Premier League.
Ahead of a meeting between Chelsea and Arsenal on Sunday, the former England international told Sky Sports: “I like him [Lacazette], I think he is a good player – but Morata is top top drawer.
"Morata is going to be an absolute star in the Premier League. He’s different class.
"I watched him come on as a sub in the first game against Burnley and even in that 15 minutes… it’s like when you watch something and someone’s done something in 15 minutes and you think 'wow, they can play' and he did that about five times. He’s hit the ground running.
"I like Lacazette don’t get me wrong, but if I was playing Real Madrid on Saturday he would play in front of Lacazette."
Arsenal spent £46 million landing Lacazette from Lyon, while Chelsea paid Real £60m for Morata.
They will likely lead their respective lines on Sunday when two old adversaries take in a crunch Premier League derby clash which could go a long way towards shaping the fortunes of Arsene Wenger and Antonio Conte this season.